In the construction of roofs, it is typical to provide means by which outdoor air can circulate along the underside of the planks of roof sheathing. Due to the high thermal efficiency of modern thermal insulation commonly used in roof constructions, moisture can get trapped under the roof and condense into the insulation. The condensed moisture can damage both the insulation and the roof sheathing and is thus undesirable. The passage of air along the underside of the roof sheathing helps prevent moisture condensation in the thermal insulation and thus increases the life of the roof.
In addition, in the absence of proper ventilation, warm air from within a building structure, such as a house, is often trapped in pockets beneath the sheathing, causing certain areas of the roof to be warmer than other areas. In cold weather, such conditions may cause ice on the roof to melt in the warm areas. The water from the melted ice flows down to cooler areas where it refreezes creating an ice dam. Additional quantities of water from the melting ice backs up behind the dam and freezes underneath the shingles or other roofing panel, causing water build up and leaks in the roof and possibly structural and cosmetic damage to the building.
In view of these problems, it is now common practice to provide air circulation vents adjacent the roof sheathing which communicate with the outdoor air and through which the outdoor air flows. A typical roof air circulation vent is provided by nailing or stapling a metal or plastic form to the roof sheathing in between pairs of adjacent roof rafters. The metal or plastic form includes flanges at opposite ends which can be nailed to the roof sheathing. Between the flanges, the form extends away from the sheathing to form an empty space between the form and the roof sheathing. Thermal insulation is either laid or blown into the space below the vent form, i.e., between the vent form and the ceiling of the building. The eaves of the roof are provided with some means for allowing the outdoor air to communicate with the vents.
U.S. Pat. No. 4,406,095, for instance, discloses a vent for placement between rafters which does not require nails or staples and which is formed in an undulated shape for added strength to prevent collapsing of the vent towards the roof sheathing under the force of thermal insulation being blown beneath the vent.
Another patent, U.S. Pat. No. 4,607,566, discloses a ventilator for placement at the eaves of the roof, between the roof sheathing and the facia board that allows outdoor air to reach the vents. The device comprises a ventilator overlying the facia board of a roof construction. This ventilator has a series of passages which allow the outdoor air to flow through it between the roof sheathing and the facia board, into the internal area of the roof construction where vents, such as the ones described in U.S. Pat. No. 4,406,095 discussed above, are positioned. This provides a path for the air along the underside of the sheathing.
The ventilator disclosed in U.S. Pat. No. 4,607,566 is complicated in structure and expensive to manufacture. Thus, it is an object of the present invention to provide a simple, low cost ventilation spacer for installation between the roof sheathing and the facia board of a roof construction to allow outdoor air to reach vents positioned along the underside of the roof sheathing.
It is another object of the present invention to provide an improved ventilation spacer for a roof construction which is simple to fabricate, install and store and which is not likely to be damaged in the ordinary course of use and handling.